This application claims priority of Korean Patent Application No. 2001-48824 filed on Aug. 13, 2001, under 35 U.S.C. xc2xa7 119, the entire disclosure of which is hereby incorporated by reference.
The present invention relates to a blue light emitting compound for organic electroluminescence and an organic electroluminescent device using the same, more particularly, to a blue light emitting compound useful in an organic electroluminescent device which is an emissive display device and has a wider viewing angle, a superior contrast ratio and a faster response time, and an organic electroluminescent device using the same.
An electroluminescent (hereinafter referred to as xe2x80x9cELxe2x80x9d) device has several advantages, including a wider viewing angle, a superior contrast ratio and a faster response time as an emissive display device.
EL devices are classified as inorganic EL devices and organic EL devices based on the material used for forming an emitting layer, wherein the organic EL device has superior luminance, driving voltage and response speed properties compared to the inorganic EL device and can be polychromed.
An ordinary organic EL device has a structure in which an anode is formed on the upper part of a substrate, and a hole transport layer, a light-emitting layer, an electron transport layer and a cathode are sequentially formed on the upper part of the anode, wherein the hole transport layer, the light-emitting layer, and the electron transport layer are organic thin films comprising organic compounds.
The operating principle of the organic EL device having the structure as described above is as follows.
A hole injected from the anode is transferred to the light-emitting layer via the hole transport layer when a voltage is applied between the anode and the cathode. On the other hand, electrons are injected into the light-emitting layer via the electron transport layer from the cathode, and carriers are recombined with each other in the region of the light-emitting layer, thereby producing exitons. The exitons are changed into the ground state from the exited state, fluorescent molecules of the light-emitting layer emit light due to the change of state, and an image is formed.
On the other hand, Eastman Kodak company has developed an organic electroluminescent device using a low molecular aromatic diamine and an aluminum complex as a material for forming the light-emitting layer for the first time in 1987 (Appl. Phys. Lett. 51, 913, 1987).
Although compounds such as diphenylanthracene, tetraphenylbutadiene, and distyrylbenzene derivatives are developed as a blue light emitting material, it is known that the compounds tend to be easily crystallized due to the poor stability of the thin film. Idemitsu Company has developed a diphenyldistyryl based blue light emitting material in which the crystallization of the compounds is hindered by the branch phenyl group so that the thin film stability is improved [H. Tikailin, H. Higashi, C. Hosokawa, EP 388, 768(1990)], and Kyushu University has developed a distyrylanthracene derivative in which the thin film stability is improved by having electron withdrawing groups and electron donating groups [PRO. SPIE, 1910, 180(1993)].
Furthermore, it is disclosed in Japanese Patent Laid-open Publication No. Heisei 10-261488 that the life cycle can be lengthened by using a distyrylarylene derivative, the electron affinity of which is between 2.6 and 3.2 electron volts(eV), as a blue light emitting compound, thereby improving the thin film stability.
However, since these compounds have lower light emitting efficiencies compared to other colored light emitting compounds and there is a further need to improve the thin film stability, it is urgently required to develop a new blue light emitting compound so as to develop a blue light emitting device or a full color light emitting device.
In order to solve the foregoing problems, it is an object of the present invention to provide a new blue light emitting compound in which light emitting efficiency properties are improved.
It is another object of the present invention to provide an organic electroluminescent device which employs the new blue light emitting compound as a color developing substance.